1. Field of Invention
This invention relates to missile systems. Specifically, the present invention relates to methods for preventing sapphire sensor housings and windows from cracking during missile flight.
2. Description of the Related Art
Advanced missile systems are used in a variety of applications ranging from explosives delivery to satellite launching. Such applications typically have stringent performance requirements. Missile sensing and tracking capability are important features affecting missile performance.
A missile may be equipped with a combination of infrared, radar, and optical sensors for missile guidance i.e., terminal homing. The sensors and accompanying sensor housings are often exposed to extreme heat loads. Sensor damage, and signal blockage often result. This is particularly true for infrared (IR) sensors. Typically an IR sensor is encased in a sapphire housing called an IR dome. At the high speeds required by many missiles, an IR dome will create a strong bow shock that results in a large pressure gradient and corresponding temperature heat load. This heating may crack the IR dome. Any resulting fracturing of the IR dome due to local heating may reduce missile performance.
To reduce the extreme temperature loads on the IR sensors and domes, a system using cooling gas was developed. Typically the system includes a pressurized canister of argon stored in the missile body. When the heat load on the IR dome becomes large, cold gas is released from the canister through a nozzle just forward of the IR dome. Unfortunately, the cold argon gas has a different refractive index than air and bends signals entering the IR dome resulting in missile tracking errors. Also, the canisters are bulky. The excess weight reduces the range of the missile, and space constraints due to the canister increase the complexity and price of the missile system. In addition, timing of the gas release with the heat load on the IR dome is difficult.
Other methods for protecting the missile from extreme heat loads and damage due to weather and particles include reducing the speed of the missile and reducing the exposure time of the IR dome. Both methods reduce missile performance. Additional methods also include placing protuberances forward of the IR dome to reduce heat loads on the IR dome. Such methods however add additional cost and weight to the missile.
Hence, there exists a need in the art for cost-effective, space-efficient system and method for preventing or reducing the cracking of missile sensor housings and windows without reducing missile performance.